I think most issues will be solved by: easy sorting. Placing items in diff "bags" and/or diff tag (Stuff to sell. Crafting. Quest.). Share inventory with party. Sell All buttom with trader. When buying: only search for items you can equip/use. Only show certain items (only ranged weapons). Only items "better than current items".
Sort by when item was found. Where item was found.
These are just mechanical stuff. The role playing with interesting merchants. Listening to their story etc should also be present.
